KStreams

Terminal Nodes

print Output debugging style information to STDOUT. Documentation.
to Send output to Kafka topic.
foreach Consume data and discard results (useful if you're writing a kafka-to-* service). Documentation.
writeAsText Output debugging style information to FILE. Documentation.

Map

flatMap Iterator returns new object with new infor (both key and value can be altered, 0 or more records returned). Documentation.
flatMapValue Iterator returns new value for same keys. Documentation.
map Iterator returns new object with new infor (both key and value can be altered, 0 or more records returned). Documentation.
mapValues Iterator returns new value for same keys. Documentation.

Joins

join Joins two streams where key == key. Subclass ValueJoiner to output joined object. Documentation.
outerJoin Join but don't require BOTH streams to have record. Documentation.
leftJoin If 'calling' or both streams have matching records, merge. If only "other" stream does, NOPE. Documentation.

Data Flow

filter If lambda function returns true, record proceeds into pipeline. Documentation.
selectKey Re-keys Kafka records. Documentation.
branch Takes a vargs of Predicates. Will return records outputted to the Predicate's topic. Documentation.
through Produces to a topic. The resulting kstream will be a producer of that same topic. Could be used to reparition data. Documentation.
transformValues Takes ValueTransformerSupplier, gets / sets StateStore. Documentation.